Whats the best course of action for a knocking engine? My first thought was to replace the spark plug, pretty sure the one thats in it now is either the original plug or one that was put in before the bike was put into storage almost 30 years ago. Any specific plugs that youve found work well? Going to redo the timing as well.

Fuel wise, I've been using 93 ethanol pump gas. Couldn't find much information on if ethanol gas causes knocking in old engines, just that it can sometimes cause them to run poorly and clog jets. Could the gas be a culprit? And are there any additives that could remedy the problem or should I just find ethanol free gas?

Finally, I read elsewhere on the forum that you can differentiate crankshaft knock from piston knock by pitch, crankshaft knock being lower and piston knock being higher, any merit to this?

So I see no one has responded. Its hard to advise on engine knocking without actually hearing your engine. But if it were me, I would order a gasket kit and a clymer manual off e-bay and start disassembly of your engine. Its better to do a full inspection of the top end and crank and not take a chance at exploding the engine and causing more damage. just my $0.02.

Clymer, CLYMER........ How very dare you!

What's wrong with the Yamaha Service Manual in the Tech Library (see link below)?

yamaha-enduros.com/index.php/workshop/se...360cc-service-manual

pinging or detonation can sound like marbles in a can or frying an egg, it will happen only under hard load, if this happens retard the ignition timing, richen the fuel mixture, or have the head modified to fix it.

piston slap sounds like a rattle at idle and when the engine is decelerating, it goes away under load.
here is my bike with piston slap:

Rod bearings going out usualy makes a really loud knock.
crankshaft main bearings will make bad vibration and sound like a low grinding/grumbling/howling.

If the rod bearing is knocking that is impending doom leading to a trashed crank & top end in a hurry!

But...most likely you're hearing piston slop. Take a video, post it on youtube, link it to this thread and people will chime in.

So far Ive only heard it at high RPMs or when revving up to high RPMs. Its not a constant noise like in your video, the best way I can describe it is like shooting a bb at or flicking a piece of metal. It also only starts making itself apparent after the bikes warmed up, so I'm guessing giving it a richer mixture would help? I have the mixture knob on the carburetor set to the 1 1/2 turns the original Yamaha owners manual suggests, if I were to go about enriching the mixture would this be the setting I would want to change, and if so, would it be a left or right turn?

I was just thinking about something I read and had it happen to me on my RT1-B....I had a strange random rattle at different RPMs. Your higher RPMs made me think of it and your exhaust on the RT3 is the same as my RT1-B. What mine was turned out to be metal to metal rattle at higher RPMs from the slip fit of the exhaust pipe into the chrome manifold that is bolted to the cylinder. Springs hold it in place but really nothing to keep it from rattling. I took an exhaust pipe expanding tool (1 1\2" I think) and slightly expanded the end of my pipe so it fit tightly into the chrome manifold. I also installed new packing in the groove where the pipe slides into. After that I was thrilled that no more rattle! I

I've also had the front screw on the chrome exhaust guard come loose and fall out leaving the guard to rattle. I used Locktite after that. Good luck hope this helps.

Listening to the '74 DT360 in the video, I think that it needs a new top end, i.e. , new piston, rings, and hone, depending on the ring clearance, and new top and bottom cylinder gaskets. Shawn Kerkes